1. Field of the Invention
The present invention relates to a linear element array having a plurality of functional elements disposed one-dimensionally, particularly such as a full-line contact type image sensor, thermal head and the like.
2. Related Background Art
A so-called linear functional image array has been adopted recently as an input/output device of a computer or a facsimile. The array with functional elements is disposed one-dimensionally and has substantially the same length as the width of an input/output medium such as an original sheet or a recording paper. For instance, an input device may be a contact type image sensor having, as functional elements, photosensors disposed linearly, and the output device may be a linear thermal head. The configuration of an input/output device whose length is substantially the same as the width of an input/output medium makes it, for example, in the case of a contact type image sensor, unnecessary to use a specific mechanical movable member which allows the optical system to be miniaturized. For this and other reasons, an input/output device of small size and high performance can be realized.
The length of a contact type image sensor or a thermal head is usually greater than A4 size (whose width is 216 mm). Therefore, a plurality of functional elements must be switched in operation by providing switching elements to respective functional elements. This is expensive and can be technically difficult. Thus, the functional elements are connected in a matrix fashion for driving them.
FIG. 1 is a circuit diagram showing an example of matrix interconnection between a plurality of functional elements. Functional elements e (1.ltoreq.i.ltoreq.N, 1.ltoreq.j.ltoreq.n) of a linear element array 1 are divided into N blocks each having n bit functional elements. A contact type image sensor uses a photosensor element as the functional element e, while a thermal head uses a heat generating element. Terminals V.sub.1 to V.sub.m, v.sub.1 to v.sub.n are connected to an unrepresented processor circuit to control (m.times.n) functional elements through their (m+n) terminals.
In the circuit arrangement of a conventional input/output device, a linear element array section 1 and a matrix circuit section 2 have been manufactured using separate linear element array and matrix wiring substrates. Thereafter, necessary circuits portion are mutually connected by means of wire bonding or the like. FIGS. 2 and 3 are diagrammatic plan and perspective views of a matrix wiring substrate. On an insulating substrate 7, first wiring layer 3, insulation layer 8 and second wiring layer 4 are formed, the first and second wiring layers 3 and 4 being connected at through-hole contacts 5. Such a matrix wiring substrate is of three-layer structure, which results in a complicated manufacturing process, low yield and hence high cost. Since there are large areas where a thin insulation layer (ordinarily thinner than 100 microns) is present between the superposing first and second wiring layers 3 and 4, capacitance between wirings becomes increased to hinder high speed operation. Further, there arises a technical problem that small current (100 to 500 mA) does not flow stably through the through-hole contact 5 due to a very thin insulation layer (likely to be formed on the first insulation layer 3, a residual portion of the insulation layer 8 and the like).